This invention relates to the field of characterizing the existence of a disease state; particularly to the utilization of mass spectroscopy to elucidate particular biopolymer markers indicative of disease state, and most particularly to specific biopolymer sequences having a unique relationship to at least one particular disease state.
Methods utilizing mass spectrometry for the analysis of a target polypeptide have been taught wherein the polypeptide is first solubilized in an appropriate solution or reagent system. The type of solution or reagent system, e.g., comprising an organic or inorganic solvent, will depend on the properties of the polypeptide and the type of mass spectrometry performed and are well known in the art (see, e.g., Vorm et al. (1994) Anal. Chem. 66:3281 (for matrix assisted laser desorption ionization MALDI) and Valaskovic et al. (1925) Anal. Chem. 67:3802 (for electrospray ionization ESI). Mass spectrometry of peptides is further disclosed, e.g., in WO 93/24834 by Chait et al.
In one prior art embodiment, the solvent is chosen so that risk that the molecules may be decomposed by the energy introduced for the vaporization process is considerably reduced, or even fully excluded. This can be achieved by embedding the sample in a matrix, which can be an organic compound, e.g., sugar, in particular pentose or hexose, but also polysaccharides such as cellulose. These compounds are decomposed thermolytically into CO2 and H2O so that no residues are formed which might lead to chemical reactions. The matrix can also be an inorganic compound, e.g., nitrate of ammonium which is decomposed practically without leaving any residues. Use of these and other solvents are further disclosed in U.S. Pat. No. 5,062,935 by Schlag et al.
Prior art mass spectrometer formats for use in analyzing the translation products include ionization (I) techniques, including but not limited to matrix assisted laser desorption (MALDI), continuous or pulsed electrospray (ESI) and related methods (e.g., IONSPRAY or THERMOSPRAY), or massive cluster impact (MCI); these ion sources can be matched with detection formats including linear or non-linear reflection time-off-light (TOF), single or multiple quadropole, single or multiple magnetic sector, Fourier Transform ion cyclotron resonance (FTICR), ion trap, and combinations thereof (e.g., ion-trap/time-of-flight). For ionization, numerous matrix/wavelength combinations (MALDI) or solvent combinations (ESI) can be employed. Subattomole levels of protein have been detected, for example, using ESI (Valaskovic, G. A. et al., (1996) Science 273:1199-1202) or MALDI (Li, L. et al., (1996) J. Am. Chem. Soc. 118:1662-1663) mass spectrometry.
ES mass spectrometry has been introduced by Fenn et al. (J. Phys. Chem. 88, 4451-59 (1984); PCT Application No. WO 90/14148) and current applications are summarized in recent review articles (R. D. Smith et al., Anal. Chem. 62, 882-89 (1990) and B. Ardrey, Electrospray Mass Spectrometry, Spectroscopy Europe, 4, 10-18 (1992)). MALDI-TOF mass spectrometry has been introduced by Hillenkamp et al. (xe2x80x9cMatrix Assisted UV-Laser Desorption/Ionization: A New Approach to Mass Spectrometry of Large Biomolecules,xe2x80x9d Biological Mass Spectrometry (Burlingame and McCloskey, editors), Elsevier Science Publishers, Amsterdam, pp. 49-60, 1990). With ESI, the determination of molecular weights in femtomole amounts of sample is very accurate due to the presence of multiple ion peaks which all could be used for the mass calculation.
The mass of the target polypeptide determined by mass spectrometry is then compared to the mass of a reference polypeptide of known identity. In one embodiment, the target polypeptide is a polypeptide containing a number of repeated amino acids directly correlated to the number of trinucleotide repeats transcribed/translated from DNA; from its mass alone the number of repeated trinucleotide repeats in the original DNA which coded it, may be deduced.
U.S. Pat. No. 6,020,208 utilizes a general category of probe elements (i.e., sample presenting means) with Surfaces Enhanced for Laser Desorption/Ionization (SELDI), within which there are three (3) separate subcategories. The SELDI process is directed toward a sample presenting means (i.e., probe element surface) with surface-associated (or surface-bound) molecules to promote the attachment (tethering or anchoring) and subsequent detachment of tethered analyte molecules in a light-dependent manner, wherein the said surface molecule(s) are selected from the group consisting of photoactive (photolabile) molecules that participate in the binding (docking, tethering, or crosslinking) of the analyte molecules to the sample presenting means (by covalent attachment mechanisms or otherwise).
PCT/EP/04396 teaches a process for determining the status of an organism by peptide measurement. The reference teaches the measurement of peptides in a sample of the organism which contains both high and low molecular weight peptides and acts as an indicator of the organism""s status. The reference concentrates on the measurement of low molecular weight peptides, i.e. below 30,000 Daltons, whose distribution serves as a representative cross-section of defined controls. Contrary to the methodology of the instant invention, the ""396 patent strives to determine the status of a healthy organism, i.e. a xe2x80x9cnormalxe2x80x9d and then use this as a reference to differentiate disease states. The present inventors do not attempt to develop a reference xe2x80x9cnormalxe2x80x9d, but rather strive to specify particular markers which are evidentiary of at least one specific disease state, whereby the presence of said marker serves as a positive indicator of disease. This leads to a simple method of analysis which can easily be performed by an untrained individual, since there is a positive correlation of data. On the contrary, the ""396 patent requires a complicated analysis by a highly trained individual to determine disease state versus the perception of non-disease or normal physiology.
Richter et al, Journal of Chromatography B, 726(1999) 25-35, refer to a database established from human hemofiltrate comprised of a mass database and a sequence database. The goal of Richter et al was to analyze the composition of the peptide fraction in human blood. Using MALDI-TOF, over 20,000 molecular masses were detected representing an estimated 5,000 different peptides. The conclusion of the study was that the hemofiltrate (HF) represented the peptide composition of plasma. No correlation of peptides with relation to normal and/or disease states is made.
As used herein, xe2x80x9canalytexe2x80x9d refers to any atom and/or molecule; including their complexes and fragment ions. In the case of biological molecules/macromolecules or xe2x80x9cbiopolymersxe2x80x9d, such analytes include but are not limited to: proteins, peptides, DNA, RNA, carbohydrates, steroids, and lipids. Note that most important biomolecules under investigation for their involvement in the structure or regulation of life processes are quite large (typically several thousand times larger than H2O.
As used herein, the term xe2x80x9cmolecular ionsxe2x80x9d refers to molecules in the charged or ionized state, typically by the addition or loss of one or more protons (H+).
As used herein, the term xe2x80x9cmolecular fragmentationxe2x80x9d or xe2x80x9cfragment ionsxe2x80x9d refers to breakdown products of analyte molecules caused, for example, during laser-induced desorption (especially in the absence of added matrix).
As used herein, the term xe2x80x9csolid phasexe2x80x9d refers to the condition of being in the solid state, for example, on the probe element surface.
As used herein, xe2x80x9cgasxe2x80x9d or xe2x80x9cvapor phasexe2x80x9d refers to molecules in the gaseous state (i.e., in vacuo for mass spectrometry).
As used herein, the term xe2x80x9canalyte desorption/ionizationxe2x80x9d refers to the transition of analytes from the solid phase to the gas phase as ions. Note that the successful desorption/ionization of large, intact molecular ions by laser desorption is relatively recent (circa 1988)xe2x80x94the big breakthrough was the chance discovery of an appropriate matrix (nicotinic acid).
As used herein, the term xe2x80x9cgas phase molecular ionsxe2x80x9d refers to those ions that enter into the gas phase. Note that large molecular mass ions such as proteins (typical mass=60,000 to 70,000 times the mass of a single proton) are typically not volatile (i.e., they do not normally enter into the gas or vapor phase). However, in the procedure of the present invention, large molecular mass ions such as proteins do enter the gas or vapor phase.
As used herein in the case of MALDI, the term xe2x80x9cmatrixxe2x80x9d refers to any one of several small, acidic, light absorbing chemicals (e.g., nicotinic or sinapinic acid) that is mixed in solution with the analyte in such a manner so that, upon drying on the probe element, the crystalline matrix-embedded analyte molecules are successfully desorbed (by laser irradiation) and ionized from the solid phase (crystals) into the gaseous or vapor phase and accelerated as intact molecular ions. For the MALDI process to be successful, analyte is mixed with a freshly prepared solution of the chemical matrix (e.g., 10,000:1 matrix:analyte) and placed on the inert probe element surface to air dry just before the mass spectrometric analysis. The large fold molar excess of matrix, present at concentrations near saturation, facilitates crystal formation and entrapment of analyte.
As used herein, xe2x80x9cenergy absorbing molecules (EAM)xe2x80x9d refers to any one of several small, light absorbing chemicals that, when presented on the surface of a probe, facilitate the neat desorption of molecules from the solid phase (i.e., surface) into the gaseous or vapor phase for subsequent acceleration as intact molecular ions. The term EAM is preferred, especially in reference to SELDI. Note that analyte desorption by the SELDI process is defined as a surface-dependent process (i.e., neat analyte is placed on a surface composed of bound EAM). In contrast, MALDI is presently thought to facilitate analyte desorption by a volcanic eruption-type process that xe2x80x9cthrowsxe2x80x9d the entire surface into the gas phase. Furthermore, note that some EAM when used as free chemicals to embed analyte molecules as described for the MALDI process will not work (i.e., they do not promote molecular desorption, thus they are not suitable matrix molecules).
As used herein, xe2x80x9cprobe elementxe2x80x9d or xe2x80x9csample presenting devicexe2x80x9d refers to an element having the following properties: it is inert (for example, typically stainless steel) and active (probe elements with surfaces enhanced to contain EAM and/or molecular capture devices).
As used herein, xe2x80x9cMALDIxe2x80x9d refers to Matrix-Assisted Laser Desorption/Ionization.
As used herein, xe2x80x9cTOFxe2x80x9d stands for Time-of-Flight.
As used herein, xe2x80x9cMSxe2x80x9d refers to Mass Spectrometry.
As used herein xe2x80x9cMALDI-TOF MSxe2x80x9d refers to Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.
As used herein, xe2x80x9cESIxe2x80x9d is an abbreviation for Electrospray ionization.
As used herein, xe2x80x9cchemical bondsxe2x80x9d is used simply as an attempt to distinguish a rational, deliberate, and knowledgeable manipulation of known classes of chemical interactions from the poorly defined kind of general adherence observed when one chemical substance (e.g., matrix) is placed on another substance (e.g., an inert probe element surface). Types of defined chemical bonds include electrostatic or ionic (+/xe2x88x92) bonds (e.g., between a positively and negatively charged groups on a protein surface), covalent bonds (very strong or xe2x80x9cpermanentxe2x80x9d bonds resulting from true electron sharing), coordinate covalent bonds (e.g., between electron donor groups in proteins and transition metal ions such as copper or iron), and hydrophobic interactions (such as between two noncharged groups).
As used herein, xe2x80x9celectron donor groupsxe2x80x9d refers to the case of biochemistry, where atoms in biomolecules (e.g, N, S, O) xe2x80x9cdonatexe2x80x9d or share electrons with electron poor groups (e.g., Cu ions and other transition metal ions).
With the advent of mass spectroscopic methods such as MALDI and SELDI, researchers have begun to utilize a tool that holds the promise of uncovering countless biopolymers which result from translation, transcription and post-translational transcription of proteins from the entire genome.
Operating upon the principles of retentate chromatography, SELDI MS involves the adsorption of proteins, based upon their physico-chemical properties at a given pH and salt concentration, followed by selectively desorbing proteins from the surface by varying pH, salt, or organic solvent concentration. After selective desorption, the proteins retained on the SELDI surface, the xe2x80x9cchipxe2x80x9d, can be analyzed using the CIPHERGEN protein detection system, or an equivalent thereof. Retentate chromatography is limited, however, by the fact that if unfractionated body fluids, e.g. blood, blood products, urine, saliva, and the like, along with tissue samples, are applied to the adsorbent surfaces, the biopolymers present in the greatest abundance will compete for all the available binding sites and thereby prevent or preclude less abundant biopolymers from interacting with them, thereby reducing or eliminating the diversity of biopolymers which are readily ascertainable.
If a process could be devised for maximizing the diversity of biopolymers discernable from a sample, the ability of researchers to accurately determine the relevance of such biopolymers with relation to one or more disease states would be immeasurably enhanced.
The instant invention is characterized by the use of a combination of preparatory steps in conjunction with SELDI mass spectroscopy and time-of-flight detection procedures to maximize the diversity of biopolymers which are verifiable within a particular sample. The cohort of biopolymers verified within a sample is then viewed with reference to their ability to evidence at least one particular disease state; thereby enabling a diagnostician to gain the ability to characterize either the presence or absence of said at least one disease state relative to recognition of the presence and/or the absence of said biopolymer.
Although all manner of biomarkers related to all disease conditions are deemed to be within the purview of the instant invention and methodology, particular significance was given to those markers and diseases associated with the complement system and Syndrome X and diseases related thereto.
The complement system is an important part of non-clonal or innate immunity that collaborates with acquired immunity to destroy invading pathogens and to facilitate the clearance of immune complexes from the system. This system is the major effector of the humoral branch of the immune system, consisting of nearly 30 serum and membrane proteins. The proteins and glycoproteins composing the complement system are synthesized largely by liver hepatocytes. Activation of the complement system involves a sequential enzyme cascade in which the proenzyme product of one step becomes the enzyme catalyst of the next step. Complement activation can occur via two pathways: the classical and the alternative. The classical pathway is commonly initiated by the formation of soluble antigen-antibody complexes or by the binding of antibody to antigen on a suitable target, such as a bacterial cell. The alternative pathway is generally initiated by various cell-surface constituents that are foreign to the host. Each complement component is designated by numerals (C1-C9), by letter symbols, or by trivial names. After a component is activated, the peptide fragments are denoted by small letters. The complement fragments interact with one another to form functional complexes. Ultimately, foreign cells are destroyed through the process of a membrane-attack complex mediated lysis.
The C4 component of the complement system is involved in the classical activation pathway. It is a glycoprotein containing three polypeptide chains (xcex1, xcex2, and xcex3). C4 is a substrate of component C1s and is activated when C1s hydrolyzes a small fragment (C4a) from the amino terminus of the a chain, exposing a binding site on the larger fragment (C4b).
The native C3 component consists of two polypeptide chains, xcex1 and xcex2. As a serum protein, C3 is involved in the alternative pathway. Serum C3, which contains an unstable thioester bond, is subject to slow spontaneous hydrolysis into C3a and C3b. The C3f component is involved in the regulation required of the complement system which confines the reaction to designated targets. During the regulation process, C3b is cleaved into two parts: C3bi and C3f. C3bi is a membrane-bound intermediate wherein C3f is a free diffusible (soluble) component.
Complement components have been implicated in the pathogenesis of several disease conditions. C3 deficiencies have the most severe clinical manifestations, such as recurrent bacterial infections and immune-complex diseases, reflecting the central role of C3. The rapid profusion of C3f moieties and resultant xe2x80x9caccidentalxe2x80x9d lysis of normal cells mediated thereby gives rise to a host of auto-immune reactions. The ability to understand and control these mechanisms, along with their attendant consequences, will enable practitioners to develop both diagnostic and therapeutic avenues by which to thwart these maladies.
In the course of defining a plurality of disease specific marker sequences, special significance was given to markers which were evidentiary of a particular disease state or with conditions associated with Syndrome-X. Syndrome-X is a multifaceted syndrome, which occurs frequently in the general population. A large segment of the adult population of industrialized countries develops this metabolic syndrome, produced by genetic, hormonal and lifestyle factors such as obesity, physical inactivity and certain nutrient excesses. This disease is characterized by the clustering of insulin resistance and hyperinsulinemia, and is often associated with dyslipidemia (atherogenic plasma lipid profile), essential hypertension, abdominal (visceral) obesity, glucose intolerance or noninsulin-dependent diabetes mellitus and an increased risk of cardiovascular events. Abnormalities of blood coagulation (higher plasminogen activator inhibitor type I and fibrinogen levels), hyperuricemia and microalbuminuria have also been found in metabolic syndrome-X.
The instant inventors view the Syndrome X continuum in its cardiovascular light, while acknowledging its important metabolic component. The first stage of Syndrome X consists of insulin resistance, abnormal blood lipids (cholesterol and triglycerides), obesity, and high blood pressure (hypertension). Any one of these four first stage conditions signals the start of Syndrome X.
Each first stage Syndrome X condition risks leading to another. For example, increased insulin production is associated with high blood fat levels, high blood pressure, and obesity. Furthermore, the effects of the first stage conditions are additive; an increase in the number of conditions causes an increase in the risk of developing more serious diseases on the Syndrome X continuum.
A patient who begins the Syndrome X continuum risks spiraling into a maze of increasingly deadly diseases. The next stages of the Syndrome X continuum lead to overt diabetes, kidney failure, and heart failure, with the possibility of stroke and heart attack at any time. Syndrome X is a dangerous continuum, and preventative medicine is the best defense. Diseases are currently most easily diagnosed in their later stages, but controlling them at a late stage is extremely difficult. Disease prevention is much more effective at an earlier stage.
Subsequent to the isolation of particular disease state marker sequences as taught by the instant invention, the promulgation of various forms of risk-assessment tests are contemplated which will allow physicians to identify asymptomatic patients before they suffer an irreversible event such as diabetes, kidney failure, and heart failure, and enable effective disease management and preventative medicine. Additionally, the specific diagnostic tests which evolve from this methodology provide a tool for rapidly and accurately diagnosing acute Syndrome X events such as heart attack and stroke, and facilitate treatment.
Accordingly, it is an objective of the instant invention to define a disease specific marker sequence which is useful in evidencing and categorizing at least one particular disease state.
It is another objective of the instant invention to evaluate samples containing a plurality of biopolymers for the presence of disease specific marker sequences which evidence a link to at least one specific disease state.
It is a further objective of the instant invention to elucidate essentially all biopolymeric moieties contained therein, whereby particularly significant moieties may be identified.
It is a further objective of the instant invention provide at least one purified antibody which is specific to said disease specific marker sequence.
It is yet another objective of the instant invention to teach a monoclonal antibody which is specific to said disease specific marker sequence.
It is a still further objective of the invention to teach polyclonal antibodies raised against said disease specific marker.
It is yet an additional objective of the instant invention to teach a diagnostic kit for determining the presence of said disease specific marker.
It is a still further objective of the instant invention to teach methods for characterizing disease state based upon the identification of said disease specific marker.
Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.